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Summer diet of two sympatric species of raptors Upland Buzzard (Buteo hemiliasius) and Eurasian Eagle Owl (Bubo bubo) in alpine meadow : problem of coexistence

Cui Q., Su J., Jiang Z.

Polish Journal of Ecology

2008

Vol. 56, nr 1

173-179

Summer diets of two sympatric raptors Upland Buzzards (Buteo hemilasius Temminck et Schlegel) and Eurasian Eagle Owls (Bubo bubo L. subsp. Hemachalana Hume) were studied in an alpine meadow (3250 m a.s.l.) on Qinghai-Tibet Plateau, China. Root voles Microtus oeconomus Pallas, plateau pikas Ochotona curzoniae Hodgson, Gansu pikas O. cansus Lyon and plateau zokors Myospalax baileyi Thomas were the main diet components of Upland Buzzards as identified through the pellets analysis with the frequency of 57, 20, 19 and 4%, respectively The four rodent species also were the main diet components of Eurasian Eagle Owls basing on the pellets and prey leftovers analysis with the frequency of 53, 26, 13 and 5%, respectively. The food niche breadth indexes of Upland Buzzards and Eurasian Eagle Owls were 1.60 and 1.77 respectively (higher value of the index means the food niche of the raptor is broader), and the diet overlap index of the two raptors was larger (C[ue] = 0.90) (the index range from 0 - no overlap - to 1 - complete overlap). It means that the diets of Upland Buzzards and Eurasian Eagle Owls were similar (Two Related Samples Test, Z = -0.752, P = 0.452). The classical resource partitioning theory can not explain the coexistence of Upland Buzzards and Eurasian Eagle Owls in alpine meadows of Qinghai-Tibet Plateau. However, differences in body size, predation mode and activity rhythm between Upland Buzzards and Eurasian Eagle Owls may explain the coexistence of these two sympatric raptors.

Carbon isotope composition of plants along altitudinal gradient and its relationship to environmental factors on the Qinghai-Tibet Plateau

Li Mingcai, Liu Hongyan, Li Laixing, Yi Xianfeng, Zhu Xiaojia

Polish Journal of Ecology

2007

Vol. 55, nr 1

67-78

Distribution pattern of [delta][^13]C values of plateau plants and their responses to environment along altitudinal gradients were investigated. In the growing season of 2003 (June-August), stable carbon isotope ratios ([delta][^13]C) of 174 plant samples belonging to 89 species of 20 families and 58 genera along the gradient 2800-4400 m (above sea level) was studied in six sites on the east edge of Qinghai-Tibet Plateau. The results indicated that the range of [delta][^13]C values of plants is narrow from -30.2[per mil] to -25.2[per mil], which means that none of the species examined belonged to C[4] photosynthetic pathway and all of these species performed C[3] photosynthetic pathway. The average [delta][^13]C values of plants at 6 sites were positively correlated to altitude (r = 0.974, P <0.01). The results revealed that site-averaged [delta][^13]C values were negatively correlated with temperature (r = 0.907, P <0.05) as well as CO[2] partial pressure (r = 0.940, P <0.01). The combination of these two factors account for 80% of the variation of [delta][^13]C values (r[^2] = 0.859, P <0.01). Varying precipitation with increasing altitude does not affect the plant [delta][^13]C values (r = 0.469, P> 0.05) as well as the sunlight duration(r = 0.630, P> 0.05).